60 



BELL SYSTEM TECHNICAL JOURNAL 



In the operation of triodes as voltage amplifiers, it is usually possible 

 to have the external load resistance large with respect to the plate 

 resistance. Consideration of equation 15 shows that this results in a 



1000 



900 



800 



700 



500 



300 



200 



100 



1000 



uj" 1400 



o 



2(0 

 < O 



oi 1200 



O - 1000 

 o 5 



<0 



z 

 < 



800 



20 



40 



60 



80 



100 120 140 

 PLATE VOLTS, Ep 



160 



180 200 220 240 



Fig. 5 — Amplification factor and transcend uctance of a screen-grid tetrode as func- 

 tions of the plate voltage. 



voltage amplification ratio approaching the amplification factor. In 

 the operation of screen-grid tubes and conventional pentodes as well, 

 which have high plate resistances, it is usually necessary that the load 

 resistances be much smaller than the plate resistances. This limitation 



